The present invention concerns a detergent dish-washing composition. This composition can be used in solid granulated or powder form but this condition is in no way necessary and the composition can also be used in any other convenient usual form, including the liquid form in special cases.
Detergent products for dish-washing are generally formulated so as to provide, after dissolution into water, a cleaning bath for removing soils of many different kinds such as vegetable fibers, protein soils, amylaceous products, dyes, tannins, burnt residues and the like; however, cleaning solutions should not simultaneously attack and corrode kitchen and dinner-ware made of glass, ceramic, china and metal. Further, cleaning solutions should be able to prevent a redeposition of mineral contaminants on the cleaned articles, such contaminants forming unpleasant films or spots on the washed surfaces.
In order to reconcile together the aforementioned requirements, the known dish-washing compositions generally contain inert or near to inert mineral salt builders whose purpose is to provide a degree of ionic strengh to the bath and to act as buffering agents. As such fillers, one can mention alkali metal sulfates, phosphates, polyphosphates, carbonates, silicates and chlorides; and other alkali salts, alkali metal salts of organic acids and neutral compounds such as urea. By virtue of their surfactive properties, polyphosphates enable the removal of certain kinds of soils, namely fatty deposits by emulsification. They also act as antiredeposition agents because of their dispersive properties and they promote the dissolving of casein with formation of sodium caseinate. The added silicates are effective for controlling the alkaline pH of the bath as a function of the concentration and of the alkali metal content thereof; they also act as corrosion inhibitors. Dish-washing compositions further contain sud-repressing surfactants and other additives such as soil-suspending ingredients, drainage promoting ingredients, perfumes, softeners and the like. A fully detailed description of the general features relative to dish-washing compositions can be found in U.S. Pat. No. 4,162,987 (MAGUIRE et al).
In addition to the above-mentioned ingredients, dish-washing composition may also comprise "chlorine donor" bleaches, i.e. products which provide active chloride after hydrolysis in the bath, said chlorine being active for oxidative and disinfection purposes. The dish-washing products may also include enzymes for catalytically hydrolyzing food residues. The most important enzymes are the proteolytic and amylolytic enzymes.
Enzymes impart a significant cleaning power to the dish-washing compositions but they are unstable in the presence of chlorine bleaches and, particularly in the case of amylolytic enzymes, they normally lose their activity in the bath at the high pH values which are normally necessary for efficient dish-washing activity.
Hence, the dish-washing detergent taught in the aforementioned U.S. Pat. No. 4,162,987 comprises enzymes but no chlorine bleach and the pH of the solution never exceeds 11.5, so as to prevent deactivation of the amylolytic enzymes (.alpha.-amylases). Such pH value is, however, only a lower limit regarding washing efficiency in dish-washers. Further, in the absence of oxidants such as the common chlorine bleaches, certain food residues, e.g. tea residues, are not sufficiently eliminated which is a major drawback.
Other prior art of some relevance includes French Pat. Nos. 1561078 & 2035547 and German DOS No. 2109389. French No. 1561078 describes laundry washing agents containing enzymes, which are stated to be active in the pH range of approximately 4 to 12. There is no clear showing of whether the pH of the washing solutions shown is in fact below 11.5. The enzymes are attached to a hydratable salt to protect the enzyme. As the patent makes manifestly clear the carbohydrases (e.g. amylase) function primarily in acid to neutral systems.
French Pat. No. 2035547 also relates to clothes laundering detergent compositions. In this patent the life of amylase enzyme is prolonged by intimate contact with starch. The detergent composition are those which in aqueous solution (0.12%) have a pH of from about 8.5 to about 11.
German (DOS) No. 2109389 also relates to protecting enzymes (during storage) utilizing certain glucose polymers in admixture with derivatives of mono-saccharides. The only mention of the pH of a laundry solution is one with a pH of 9.